6.5. Module Trailer

The module trailer is optional, comes right at the end of
the grammar file, and takes the same form as the module
header:

{
<Haskell code>
}

This section is used for placing auxiliary definitions
that need to be in the same module as the parser. In small
parsers, it often contains a hand-written lexical analyser too.
There is no restriction on what can be placed in the module
trailer, and any code in there is copied verbatim into the
generated parser file.